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authorRick Edgecombe <rick.p.edgecombe@intel.com>2023-06-13 03:10:27 +0300
committerRick Edgecombe <rick.p.edgecombe@intel.com>2023-07-12 00:10:56 +0300
commit2f0584f3f4bd60bcc8735172981fb0bff86e74e0 (patch)
tree4b44c18c722db9e18f7738995fa419f3bc1fe2ea /Documentation/mm
parent06c2afb862f9da8dc5efa4b6076a0e48c3fbaaa5 (diff)
downloadlinux-2f0584f3f4bd60bcc8735172981fb0bff86e74e0.tar.xz
mm: Rename arch pte_mkwrite()'s to pte_mkwrite_novma()
The x86 Shadow stack feature includes a new type of memory called shadow stack. This shadow stack memory has some unusual properties, which requires some core mm changes to function properly. One of these unusual properties is that shadow stack memory is writable, but only in limited ways. These limits are applied via a specific PTE bit combination. Nevertheless, the memory is writable, and core mm code will need to apply the writable permissions in the typical paths that call pte_mkwrite(). The goal is to make pte_mkwrite() take a VMA, so that the x86 implementation of it can know whether to create regular writable or shadow stack mappings. But there are a couple of challenges to this. Modifying the signatures of each arch pte_mkwrite() implementation would be error prone because some are generated with macros and would need to be re-implemented. Also, some pte_mkwrite() callers operate on kernel memory without a VMA. So this can be done in a three step process. First pte_mkwrite() can be renamed to pte_mkwrite_novma() in each arch, with a generic pte_mkwrite() added that just calls pte_mkwrite_novma(). Next callers without a VMA can be moved to pte_mkwrite_novma(). And lastly, pte_mkwrite() and all callers can be changed to take/pass a VMA. Start the process by renaming pte_mkwrite() to pte_mkwrite_novma() and adding the pte_mkwrite() wrapper in linux/pgtable.h. Apply the same pattern for pmd_mkwrite(). Since not all archs have a pmd_mkwrite_novma(), create a new arch config HAS_HUGE_PAGE that can be used to tell if pmd_mkwrite() should be defined. Otherwise in the !HAS_HUGE_PAGE cases the compiler would not be able to find pmd_mkwrite_novma(). No functional change. Suggested-by: Linus Torvalds <torvalds@linuxfoundation.org> Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com> Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com> Reviewed-by: Mike Rapoport (IBM) <rppt@kernel.org> Acked-by: Geert Uytterhoeven <geert@linux-m68k.org> Acked-by: David Hildenbrand <david@redhat.com> Link: https://lore.kernel.org/lkml/CAHk-=wiZjSu7c9sFYZb3q04108stgHff2wfbokGCCgW7riz+8Q@mail.gmail.com/ Link: https://lore.kernel.org/all/20230613001108.3040476-2-rick.p.edgecombe%40intel.com
Diffstat (limited to 'Documentation/mm')
-rw-r--r--Documentation/mm/arch_pgtable_helpers.rst6
1 files changed, 6 insertions, 0 deletions
diff --git a/Documentation/mm/arch_pgtable_helpers.rst b/Documentation/mm/arch_pgtable_helpers.rst
index af3891f895b0..69ce1f2aa4d1 100644
--- a/Documentation/mm/arch_pgtable_helpers.rst
+++ b/Documentation/mm/arch_pgtable_helpers.rst
@@ -48,6 +48,9 @@ PTE Page Table Helpers
+---------------------------+--------------------------------------------------+
| pte_mkwrite | Creates a writable PTE |
+---------------------------+--------------------------------------------------+
+| pte_mkwrite_novma | Creates a writable PTE, of the conventional type |
+| | of writable. |
++---------------------------+--------------------------------------------------+
| pte_wrprotect | Creates a write protected PTE |
+---------------------------+--------------------------------------------------+
| pte_mkspecial | Creates a special PTE |
@@ -120,6 +123,9 @@ PMD Page Table Helpers
+---------------------------+--------------------------------------------------+
| pmd_mkwrite | Creates a writable PMD |
+---------------------------+--------------------------------------------------+
+| pmd_mkwrite_novma | Creates a writable PMD, of the conventional type |
+| | of writable. |
++---------------------------+--------------------------------------------------+
| pmd_wrprotect | Creates a write protected PMD |
+---------------------------+--------------------------------------------------+
| pmd_mkspecial | Creates a special PMD |